Stress urinary incontinence (SUI), defined as involuntary loss of urine on physical exertion, sneezing, or coughing,1 is a common disorder in the female population with its highest prevalence in women between 25 and 49 years of age.2,3 As a consequence, many afflicted women are of fertile age and may be exposed to future deliveries. Midurethral sling surgery is a minimally invasive surgical technique for the treatment of SUI with subjective and objective cure rates between 75% and 94%.4–6 The procedure may use either a retropubic or transobturator approach with near-equivalent success rates.7,8 Many clinicians consider a future pregnancy as a relative contraindication for incontinence surgery and would suggest either to postpone surgery or recommend cesarean delivery as the preferred mode of delivery for a woman with a previous midurethral sling procedure.9,10 However, the scientific evidence to substantiate any recommendations is scarce. Current literature regarding pregnancy after SUI surgery consists of retrospective case series, the largest of which includes 26 patients.11
Using nationwide health care registers, we identified a cohort of women who became pregnant and delivered a neonate after a midurethral sling procedure and a matched control group including women with no childbirths after surgery. The aim of this study was to assess whether subsequent childbirths affect the outcomes of midurethral sling surgery with regard to SUI and lower urinary tract symptoms.
MATERIALS AND METHODS
We performed a population-based cohort study. To identify our study population, we used data from nationwide health care registers supervised by the Swedish Board of Health and Welfare (www.socialstyrelsen.se/english). Individual records are based on the unique national registration number individually assigned to all nationals at birth or immigration, which also allows linkage across registers. The Swedish Medical Birth Register was founded in 1973 and includes data on practically all (99%) deliveries in Sweden (http://www.socialstyrelsen.se/publikationer2003/2003-112-3). The Patient Register, initiated in the 1960s, has complete national coverage from 1987 and includes all inpatient care in Sweden. The register contains data on individual hospital discharges and surgical procedure codes according to the Swedish Classification of Surgical Procedures. The records also contain dates of admission, discharge, and date of surgery. The register has been validated12 and has a less than 1% yearly loss to registration, and correct coding for surgical procedures is achieved in 98% of cases.
From the Patient Register, we identified women who had undergone a midurethral sling procedure (retropubic sling code LEG 10; transobturator sling code LEG 13) between 2002 and 2014. By record linkage with the Medical Birth Register, we subsequently identified those who had had one or more subsequent deliveries (study group; n=207). For every woman in the study group, we then randomly identified a maximum of three controls (n=521) per case using an identical selection process. The women in the control group had no deliveries after their midurethral sling procedure and were matched to the women in the case group by year of surgery and age at surgery. From the Swedish address Register, we retrieved up-to-date addresses for the study participants.
In June 2016, questionnaires were sent out to both the study and control groups. A reminder was sent out in November 2016 to those who had not replied. The questionnaire included information on demographic data such as length, current weight, smoking status, parity and mode of deliveries, comorbidities (including psychiatric disorders and current medications) as well as condition-specific validated questionnaires. To assess the degree of bother from lower urinary tract symptoms, we used the Urogenital Distress Inventory13 and the short form of the Incontinence Impact Questionnaire.14 The study group was also requested to answer additional questions concerning the need for catheterization as a result of bladder-emptying difficulties during the pregnancy after midurethral sling surgery.
The Urogenital Distress Inventory consists of three subscales (each ranging from 0 to 100 with a maximum summary score of 300) reflecting the presence and bother from different aspects of urogenital dysfunction: SUI symptoms, irritative symptoms, and obstructive symptoms; higher scores indicate greater dysfunction. The Incontinence Impact Questionnaire includes 30 questions and was designed to assess the effect of urinary incontinence (UI) on activities and emotions in women. A short form consisting of seven items (IIQ-7) has proven to accurately predict the Incontinence Impact Questionnaire long-form total score.14 The score calculated from the Incontinence Impact Questionnaire ranges from 0 to 100 with higher scores indicating greater effect on quality of life.
Our primary outcome was symptomatic SUI, defined as an answer of moderate to great bother on the question “Do you experience urine leakage related to physical activity, coughing or sneezing?” (Urogenital Distress Inventory). No symptoms or only little bother from symptoms were categorized as no SUI. We tested the robustness of this definition by comparing differences in median Incontinence Impact Questionnaire scores between the SUI group and the no SUI group. We also performed a sensitivity analysis by changing the cutoff point at “no symptoms” compared with “little to greatly bothersome symptoms.” Secondary outcomes included the total Urogenital Distress Inventory score, Urogenital Distress Inventory subscale scores, and Incontinence Impact Questionnaire scores, as well as patient-reported need for catheterization during pregnancy after midurethral sling surgery and whether patients reported that midurethral sling surgery was an indication for cesarean delivery. Lastly we also tested whether different demographic variables, such as body mass index (BMI, calculated as weight (kg)/[height (m)]2), total parity, smoking status, menopausal status, presence of a comorbidity or a psychiatric disorder, a secondary midurethral sling surgery, previous prolapse surgery, or hysterectomy, were associated with the primary outcome (presence of symptomatic SUI).
Statistical analyses were performed using IBM SPSS Statistics 23. Baseline characteristics are presented as medians with range or interquartile ranges for continuous variables and as frequencies for categorical variables. For comparison of baseline variables between groups, we used the Mann–Whitney U test when analyzing continuous data and Fisher exact test for categorical variables. Categorical endpoints were analyzed using univariate and multivariate logistic regression. The multivariate regression model adjusted for variables with a significant difference in the crude regression analysis: BMI, parity, psychiatric disorder, a secondary midurethral sling surgery, and previous prolapse surgery. Results of the logistic regression analyses are presented as crude and adjusted odds ratios (ORs) with 95% CIs. Secondary endpoints such as questionnaire scores were analyzed using the Mann–Whitney U test. A P value of <.05 was considered significant for all comparisons. The study was approved by the Research Ethics Committee at Karolinska Institutet, Stockholm, Sweden, and conforms to the STrengthening the Reporting of OBservational studies in Epidemiology guidelines for reporting observational studies (www.strobe-statement.org).
Figure 1 shows a flowchart of the study participants. A total of 728 women were eligible for the study. The overall response rate to the questionnaire was 74% and a total of 163 (79%) women with childbirth after midurethral sling surgery and 374 (72%) women in a control group were included in the final analysis. A sensitivity analysis comparing age at time of the study, number of years postoperative and postpartum as well as age and concomitant prolapse surgery at the time of primary midurethral sling procedure showed no differences between the responders and nonresponders (data not shown). A total of 141 of the women in the study group had one delivery (86%), 21 (13%) had two deliveries, and one woman (1%) had three deliveries after their initial midurethral sling procedure.
Demographic characteristics are presented in Table 1. There were no significant differences between the study group and the control group except for number of years postpartum and total parity. When comparing women with vaginal and cesarean delivery after a midurethral sling procedure, the groups were also similar regarding demographic characteristics except for parity and smoking status (Table 1).
There were no significant differences between women with childbirths and those without after a midurethral sling procedure with regard to lower urinary tract symptoms (Table 2). In a logistic regression analysis, factors associated with the presence of SUI symptoms were obesity (BMI 30 or greater), a history of a secondary midurethral sling surgery, or a history of pelvic organ prolapse surgery and psychiatric disorders (Table 2).
When comparing women with vaginal delivery and cesarean delivery as mode of delivery after a midurethral sling procedure, there were no differences between the groups with regard to the primary outcome. A total of 22% in both groups reported SUI (adjusted OR 0.6, 95% CI 0.2–1.4, P=.24). In the study group, 3 of 163 women (1.8%) reported a need for bladder catheterization during the pregnancy subsequent to a midurethral sling procedure. Of women with a cesarean delivery after a midurethral sling procedure, 73 of 95 (77%) reported the sling procedure as the indication for cesarean delivery.
A comparison of Urogenital Distress Inventory and Incontinence Impact Questionnaire scores between the study group and the control group as well as between women with vaginal delivery compared with cesarean delivery within the study group is presented in Table 3. Figure 2 illustrates a visual comparison of Urogenital Distress Inventory domain scores and Incontinence Impact Questionnaire scores in box plots, displaying medians, interquartile ranges, and outliers.
In a sensitivity analysis, we changed the cutoff for SUI to include a range from little to greatly bothersome symptoms. According to that definition, a total of 52% of the women in the study group reported no SUI compared with 55% in the control group. In univariate and multivariate logistic regression analyses, there were no differences between the groups (adjusted OR 1.0, 95% CI 0.6–1.5). The median Incontinence Impact Questionnaire score in the no SUI group was 0 as compared with 22 in the SUI group.
We found that childbirth after a midurethral sling procedure was not associated with a higher rate of patient-reported SUI compared with women with no deliveries after surgery. This is a large study that addresses this subject and also includes a control group. Previous studies consist of case reports or case series as well as reviews of the same with associated methodologic limitations. The rate of SUI in our study group (22%) is in concordance with most previous reports as well as a recent review article by Cavkaytar et al15 in which 83% of women with childbirth after a successful midurethral sling application remained continent. These findings thus suggest that a less restrictive attitude to surgical treatment may be adopted when counseling women with bothersome SUI who may not have completed childbearing.
Another clinically relevant question for both gynecologists and obstetricians is whether mode of delivery after a midurethral sling procedure influences the risk of postpartum SUI. Previous reports have not demonstrated a difference in postpartum SUI when comparing vaginal childbirth and cesarean delivery in women with a previous midurethral sling procedure.11,15 However, because of the limited data, there has been no consensus on preferable mode of delivery in these patients. We found no evidence to suggest that vaginal delivery after midurethral sling surgery is associated with a higher risk of recurrent SUI or any other lower urinary tract symptoms in comparison with cesarean delivery. The results indicate that polypropylene mesh tape and endogenous fibrous tissue fixation are robust enough to maintain their function despite the morphologic changes during pregnancy and vaginal delivery. In concurrence with previous studies, pregnancy-related complications possibly related to a previous midurethral sling procedure were very low.11,15
Several variables were associated with the presence of SUI symptoms after childbirth after a midurethral sling procedure. Obesity is considered an established risk factor for SUI,16 but studies evaluating whether obesity affects failure rates after midurethral sling surgery show conflicting results.17,18 In the present study, obesity increased the risk of SUI after childbirth among women with a previous midurethral sling procedure. The prevalence of psychiatric illness in our study population was consistent with rates in the general Swedish population and in previous epidemiologic studies on UI.19,20 Melville et al20 report that, in patients with UI, comorbid psychiatric illness was associated with symptom amplification, a significantly lower incontinence-specific quality of life, and worse functional status. Consistent with the present study, concomitant prolapse surgery and secondary midurethral sling procedures have also been associated with significantly higher failure rates.21
Because delivery after midurethral sling surgery is still relatively uncommon, there is a paucity of data on this subject. A strength of this study is the relatively large sample size. Another strength is that the outcomes were compared with a matched control group and not with previous studies. Considering that this is a population-based study, with patients treated in a routine clinical setting by gynecologic surgeons throughout Sweden, one could argue that the generalizability of our findings is high. Further strengths of this study are that patient-reported symptoms were evaluated using validated questionnaires and that the effect of symptoms on quality of life was assessed. A common issue with questionnaire-based studies is unsatisfactory response rates, which might introduce bias. In this study, the overall response rate was 74%, which suggests that the risk of selection bias is low.22 Our sensitivity analysis also supports this assumption given the lack of significant differences between responders and nonresponders.
The lack of objective outcomes is a limitation of this study. However, when assessing incontinence and treatment outcomes, symptom relief is widely considered the primary outcome, regardless of objective outcomes.23 The Urogenital Distress Inventory and Incontinence Impact Questionnaire have been shown to significantly correlate with the number of UI episodes and pads used per week24 and are “highly recommended” by the International Consultation on Incontinence as robust and appropriate questionnaires for evaluating symptoms and the quality-of-life effect of UI.25 We do not have data on postoperative continence status after the primary midurethral sling procedure in our exposed group. Therefore, we cannot comment on the proportion of women who had a recurrence of symptoms as a result of the exposure of pregnancy and delivery, which would have provided important information.
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